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[2a01:4f8:120:2468::2]) by smtp.gmail.com with ESMTPSA id l23sm9684536wme.22.2021.07.20.03.24.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jul 2021 03:24:28 -0700 (PDT) From: =?utf-8?b?w4Z2YXIgQXJuZmrDtnLDsCBCamFybWFzb24=?= To: git@vger.kernel.org Cc: Junio C Hamano , Jeff King , Han-Wen Nienhuys , Michael Haggerty , =?utf-8?b?w4Z2YXIgQXJuZmrDtnLDsCBC?= =?utf-8?b?amFybWFzb24=?= Subject: [PATCH v3 08/12] refs/files: add a comment about refs_reflog_exists() call Date: Tue, 20 Jul 2021 12:24:13 +0200 Message-Id: X-Mailer: git-send-email 2.32.0.874.ge7a9d58bfcf In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Add a comment about why it is that we need to check for the the existence of a reflog we're deleting after we've successfully acquired the lock in files_reflog_expire(). As noted in [1] the lock protocol for reflogs is somewhat intuitive. This early exit code the comment applies to dates all the way back to 4264dc15e19 (git reflog expire, 2006-12-19). 1. https://lore.kernel.org/git/54DCDA42.2060800@alum.mit.edu/ Signed-off-by: Ævar Arnfjörð Bjarmason --- refs/files-backend.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/refs/files-backend.c b/refs/files-backend.c index ce4b3fb1c7a..92f49cfb7d4 100644 --- a/refs/files-backend.c +++ b/refs/files-backend.c @@ -3068,6 +3068,19 @@ static int files_reflog_expire(struct ref_store *ref_store, strbuf_release(&err); return -1; } + + /* + * When refs are deleted, their reflog is deleted before the + * ref itself is deleted. This is because there is no separate + * lock for reflog; instead we take a lock on the ref with + * lock_ref_oid_basic(). + * + * If a race happens and the reflog doesn't exist after we've + * acquired the lock that's OK. We've got nothing more to do; + * We were asked to delete the reflog, but someone else + * deleted it! The caller doesn't care that we deleted it, + * just that it is deleted. So we can return successfully. + */ if (!refs_reflog_exists(ref_store, refname)) { unlock_ref(lock); return 0;